android 进度条未正确更新进度（onPostExecute() 运行较晚）

Question

我正在构建一个用于从 Internet 下载文件的练习和学习应用程序。我确信将来我将不得不对其进行许多更改，但到目前为止，我无法正确更新进度条。当我单击按钮时，应该运行 AsyncTask 子类并获取文件。当从 Internet 读取文件时，进度条应该会更新。问题是，有时进度条似乎立即全部更新，有时它会滞后很长时间保持空白，直到再次，一次全部更新。我发现我使用 buffer.size() 作为 publishProgress() 的参数存在问题，但我不确定如何正确执行此操作。 onPostExecute() 也需要很长时间才能运行。作为一个附带问题，我有一小段代码我注释掉了，它使用 rxjava 来更新进度条。我正在考虑尝试使用类似的东西来替换 onPostExecute()。那会是个坏主意吗？这是“rxjava 的正确用法吗？”这是我的 MainActivity：

public class MainActivity extends AppCompatActivity {

private static final String TAG = "MAIN";
private static final String startURL = "https://www.google.com";
private static final int REQUEST_CODE_EXTERNAL = 0;

private Button runButton;
private EditText urlSpecBox;
private ProgressBar progressBar;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //request for permission to write to storage here
    if(ContextCompat.checkSelfPermission(getApplicationContext(), Manifest.permission.WRITE_EXTERNAL_STORAGE)
            != PackageManager.PERMISSION_GRANTED){
        ActivityCompat.requestPermissions(this, (new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}), REQUEST_CODE_EXTERNAL);
    }

    progressBar = (ProgressBar) findViewById(R.id.progroessBar);
    progressBar.setMax(100);


    runButton = (Button) findViewById(R.id.dwnldButton);
    runButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            try{
                progressBar.setVisibility(View.VISIBLE);
                progressBar.setProgress(0);
                new AsyncDownload(new URL(startURL), progressBar).execute();

            }catch (MalformedURLException me){
                Log.e(TAG, "error with url", me);
            }
        }
    });

    urlSpecBox = (EditText) findViewById(R.id.urlSpecBox);

}
}

和我的 asynctask 子类：

public class AsyncDownload extends AsyncTask<Void, Integer, Void>{
private static final String TAG = "AsyncDownload";
private static final String STORAGE_LOCATION = "/sdcard/"; //android directory picker is needed

private URL url;
private ProgressBar mProgessBar;
//private ArrayList<Byte> bytes = new ArrayList<>();

public AsyncDownload(URL url, ProgressBar progressBar){
    mProgessBar = progressBar;
    this.url = url;
}

@Override
protected void onProgressUpdate(Integer... progress){
    mProgessBar.setProgress(progress[0]);
}

@Override
protected Void doInBackground(Void... params){

    try{
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));

        ByteArrayOutputStream buffer = new ByteArrayOutputStream();

        int c;
        while ((c = in.read()) != -1){
            buffer.write(c);
            publishProgress(buffer.size());
        }

        Log.i(TAG,  "response received");

        Random rand = new Random(4L);
        String temp = String.valueOf(rand.nextInt());

        String finalLocation = STORAGE_LOCATION + temp;

        File file = new File(finalLocation);
        file.getParentFile().mkdirs();

        Log.i(TAG, file.getName());

        FileOutputStream fOut = new FileOutputStream(file);
        fOut.write(buffer.toByteArray());
        buffer.close();
        fOut.flush();
        fOut.close();
        FileInputStream fIn = new FileInputStream(finalLocation);

        String reRead = new String();
        int a;
        while ((a = fIn.read()) != -1){
            reRead += a;
        }

        Log.i(TAG, "reRead" + reRead);

        //this section is for automatic file naming
        /*Random rand = new Random(5L);
        String fileNumber = String.valueOf(rand.nextInt());
        StringBuilder sb = new StringBuilder();
        sb.append(fileNumber).append("download"); //definitely needs work

        Log.i(TAG, sb.toString());*/

        //FileOutputStream fOut = new FileOutputStream()

    }catch (IOException ioe){
        Log.e(TAG, "network error" + ioe.toString(), ioe);
    }

    /*rx.Observable.just(0) //is it correct to use rxjava this way?
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(
                    new Action1<Integer>() {
                        @Override
                        public void call(Integer integer) {
                            mProgessBar.setProgress(integer);
                            mProgessBar.setVisibility(View.VISIBLE);
                        }
                    }
            );*/

    return null;
}

@Override
protected void onPostExecute(Void result){ // METHOD IS NEVER CALLED
    super.onPostExecute(result);
    Log.i(TAG, "onPostExecute called! - Task Completed!");
    mProgessBar.setProgress(0);
    mProgessBar.setVisibility(View.GONE);
}

}

如果我的问题似乎不清楚，我深表歉意。我要问的基本上是如何更有效地执行与从 Internet 读取相关的进度更新，并减少调用 doInBackground() 和调用 onPostExecute() 之间的延迟。

修改我的代码：

int c;
        int progress = 0;
        int count = buffer.size();
        int fileSize = connection.getContentLength();

        while ((c = in.read()) != -1){
            buffer.write(c);
            try{
                Thread.sleep(TimeUnit.MILLISECONDS.toMillis(100L));
            }catch (InterruptedException ie){
                Log.e(TAG, "thread interrupted", ie);
            }finally {
                if (count > 0){
                    publishProgress((int) ((progress+=count)*100/fileSize));
                }
            }
            //publishProgress(buffer.size());
        }

Answer 1

你有延迟，因为你在一个循环中公开进度，它会让主线程多次调用它。我们在这里有一些解决方案：

1. 请延迟使用 Thread.sleep。至少一亿。

   试试{ 线程.sleep(100); }catch (InterruptedException e){ }最后 { 如果（文件长度> 0）{ this.publishProgress((int) ((progress +=count) * 100 / fileLength)); } }

2. 与之前的百分比相比增加 1% 时的公开进度。

3. 更新代码：不需要使用缓冲区

   FileOutputStream fOut = new FileOutputStream(file);
   FileInputStream fIn = new FileInputStream(finalLocation);
   byte data[] = new byte[4096];
   long progress = 0;
   int count;
   int fileSize = connection.getContentLength();
   
   while ((c = in.read()) != -1){
       //we should write the data before publish progress
       fOut.write(data, 0, count)
       try{
           Thread.sleep(100);
       }catch (InterruptedException ie){
           Log.e(TAG, "thread interrupted", ie);
       }finally {
           if (fileSize > 0){
               publishProgress((int) ((progress+=count)*100/fileSize));
           }
       }
   }
   

或

if (fileSize > 0) {
    currentProgress = ((progress += count) * 100 / fileSize);
    // Publish only on increments of 1%
    if (currentProgress >= previousProgress + 1) {
        this.publishProgress(currentProgress);
        previousProgress = currentProgress;
    }

}

Answer 2

在你的 AsyncDownload 类中使用它

@Override
        protected void onProgressUpdate(Integer... values) {
            progressBar.setProgress(values[0]);
        }